/*
 * Copyright (c) 2002 Sun Microsystems, Inc.  All rights
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:
 *       "This product includes software developed by the
 *       Sun Microsystems, Inc. for Project JXTA."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Sun", "Sun Microsystems, Inc.", "JXTA" and "Project JXTA" must
 *    not be used to endorse or promote products derived from this
 *    software without prior written permission. For written
 *    permission, please contact Project JXTA at http://www.jxta.org.
 *
 * 5. Products derived from this software may not be called "JXTA",
 *    nor may "JXTA" appear in their name, without prior written
 *    permission of Sun.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL SUN MICROSYSTEMS OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of Project JXTA.  For more
 * information on Project JXTA, please see
 * <http://www.jxta.org/>.
 *
 * This license is based on the BSD license adopted by the Apache Foundation.
 *
 * $Id: Dlink.java,v 1.1 2005/05/11 02:27:09 hamada Exp $
 *
 */

package net.jxta.impl.util;

/**
 * A dlinkable base class.
 * It is far less general than java's LinkedList but permits much better
 * removal performance from the middle of the list because a contained
 * element and the corresponding chaining object are one and the same.
 *
 * The major inconvenient of this class is that it is...a class, not an
 * interface. Making it an interface does not make sense since one would have
 * to re-implement it entirely. There is almost no value added in a List class
 * in addition to a Link class. A list of these Dlink is just a stand-alone
 * Dlink with just a couple of additional convenience methods.
 */

public class Dlink {

    /**
     * Previous element in list.
     */
    private Dlink prev;

    /**
     * Next element in list.
     */
    private Dlink next;

    private void setNext(Dlink n) {
	next = n;
    }

    private void setPrev(Dlink p) {
	prev = p;
    }

    public Dlink next() {
	return next;
    }

    public Dlink prev() {
	return prev;
    }

    public void unlink() {
	next.setPrev(prev);
	prev.setNext(next);
	next = prev = this;
    }

    public boolean isLinked() {
	return next != this;
    }

    public void linkNewNext(Dlink ne) {
	ne.unlink();
	ne.setPrev(this);
	ne.setNext(next);
	next.setPrev(ne);
	next = ne;
    }

    public void linkNewPrev(Dlink ne) {
	ne.unlink();
	ne.setNext(this);
	ne.setPrev(prev);
	prev.setNext(ne);
	prev = ne;
    }

    public Dlink() {
	next = prev = this;
    }
}
